Influence of soluble polymer residues in crosslinked carboxymethyl starch on some physical properties of its hydrogels

Autor(en): Hess, Christoph
Hartmann, Brigitte
Lechner, M. Dieter
Nierling, Wolfgang
Seidel, Christian
Kulicke, Werner-Michael
Stichwörter: absorption under load; carboxymethyl starch; Food Science & Technology; free swelling capacity; hydrogel
Erscheinungsdatum: 2007
Herausgeber: WILEY-V C H VERLAG GMBH
Journal: STARCH-STARKE
Volumen: 59
Ausgabe: 9
Startseite: 423
Seitenende: 429
Zusammenfassung: 
Crosslinked carboxymethyl starch (CMS) was synthesized from potato starch in a single-step procedure with mono- (MCA) and clichloroacetic acid (DCA), using the well-known Williamson reaction. The products varied in their degree of substitution DS (average number of carboxymethyl groups per monomer unit) and crosslinker ratio F, (number of crosslinker molecules offered per monomer unit). After neutralizing and removal of the formed salt, one part of the synthesized CMS networks was pre-swollen in water in an additional purification step in order to wash out unlinked, soluble polymer chains. The rest of the product remained unwashed. Different swelling experiments were performed with the two samples, before being dried and ground. Both, the Free Swelling Capacity (FSC) and the Absorption Capacity Under Mechanical Load (AUL) of the hydrogels were strongly influenced by chemically unlinked CMS chains that were only physically entangled in the network structure. These mobile polymer segments were responsible for a significant weight loss of the swollen, unwashed hydrogels over the course of time. Rheological oscillatory experiments showed that, in order to achieve comparable values for the storage and loss moduli (G' and G''), the polymer content of an unwashed hydrogel had to be more than twice as high as that of the corresponding purified product. By using a special rheological test procedure with a cyclic temperature program, the long-term stability of CMS gels could be measured and verified.
ISSN: 00389056
DOI: 10.1002/star.200400383

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